Tyrannosaurus Trackways Reveal a Dinosaur's Walk

Scientists have found tyrannosaur footprints before, but never a trackway that reveal the dino's gait over multiple steps. Until now.

Scientists have discovered the first tyrannosaurus trackways—groups of footprints that reveal its path. While individual footprints have been found before, these newfound 70-million-year-old fossils are the first known trackways of tyrannosaurs. The evidence provides the first record of the carnivore's gait, and reveals that these great carnivores may not have been lone hunters but, rather, walked together.

The trackways, outlined in a study in the journal PLoS One today, were discovered in the forests of northeastern British Columbia in 2011. There are three in total—one has three prints, while the other two have two. They were all made in clay-rich sandstone, which preserved the tracks so well that they have impressions of the scales on the skin of these dinosaurs.

Their shape identifies them as belonging to carnivorous dinosaurs, and their size reveals they belonged to tyrannosaurs, the largest carnivorous dinosaurs in that area. Judging by their size, the researchers estimate the track makers were 25, 26, and 29 years old. One of the track makers had the right toe on its left foot reduced to just a nub, suggesting it was wounded at one point in its life. At least three kinds of tyrannosaurs from that time and region were large enough to create these tracks—Albertosaurus, Gorgosaurus, and Daspletosaurus—but the scientists cannot say for sure which of these dinosaurs actually left these footprints.

These three-toed footprints are up to 26.3 inches long, and the paces of these dinos were up to 68.3 inches long. From this the researchers calculate that a T. rex's hips were about 7.5 to 9.4 feet high as they walked. From the prints the researchers estimate the tyrannosaurs were walking at speeds of about 3.9 to 5.2 mph.

R. McCrea

Image from a silicon mold of a tyrannosaur trackway. (Photo by R. McCrea)

"There were some very birdlike aspects to their locomotion," says lead study author Richard McCrea, a paleontologist at the Peace Region Palaeontology Research Centre in Tumbler Ridge, Canada. "If humans walked on a surface like this, they would probably pull through the sediment as they drew their foot forward, but these tyrannosaurs drew their feet backward—a very birdlike movement of the limb."

"However, that's where the comparison with birds ends," McCrea adds. "They had a very narrow trackway, putting one foot in front of the other, not at all what you'd see with birds or people." He says that previous models of tyrannosaurus locomotion didn't suggests such a narrow way of walking, so these trackways could lead to a new understanding of how the tyrannosaurs moved around.

The prints were apparently all made at about the same time. This suggests they were left by tyrannosaurs walking alongside each other. "This is the strongest evidence we can have of gregarious behavior among tyrannosaurs," McCrea says. "Trackways are the closest we can get to observing the behavior of dinosaurs, other than getting in a time machine and going back in time to observe them in person."

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